Thursday, August 10, 2017

Dammed Wildlife

The Kickemuit River Fish Ladder was built on the Warren Reservoir to give migrating river herring access to the pond.

By Rachel Calabro, Save The Bay Riverkeeper

Imagine you are a river fish. To thrive in your environment, you have a few requirements. Cool water with enough oxygen will keep you alert and active. Insects that wash downstream or emerge from the stream bottom will keep you fed. Sand and gravel in which to lay your eggs and plenty of places to hide from predators are also keys to survival. When rivers function properly, all these things are in place to support a wide diversity of fish and insects.

But when environmental stresses, such as low water levels or warm water, are present, fish need places to go for refuge. Just like on a hot sunny day you might seek the shade of a tree, fish seek out cold spots in deep pools and under bits of wood in the stream. Fish also need to find mates to increase their genetic diversity and species health. A healthy population of fish will be able to migrate up and downstream and into tributary streams to mix and mingle with others of their species and to find new habitat. These are all parts of a healthy stream ecosystem.

An historic photo of Pawtuxet Bridge and falls before the dam was removed in 2011.

Dams, culverts and other physical changes to a stream can cause harm not only to the species living there, but also to the quality of the water and habitat for other wildlife and surrounding ecosystems. Dams change the dynamics of a stream by slowing the water, allowing fine sediment to deposit rather than flow downstream, and changing both temperature and nutrients in the water. Warm water holds less oxygen. Gravels are covered over by fine silts and sands. In essence, a dam turns a river into a pond. Fish that thrive in ponds move in to the newly created habitat, cutting off the upstream habitat from the fish living in the river below. As a result, genetic diversity suffers, and less food comes downstream. The community of river fish changes as well.

Humans have caused many changes to our surrounding environment, but few of our changes to streams and rivers have had as much consequence as dams. Although beavers have made dams for thousands of years, altering the landscape in many ways, these dams are temporary and an important part of creating a constantly changing set of diverse wetland systems. Our wildlife adapt and thrive with these changes. Most of our man-made dams no longer serve their original purpose of providing power for mills. They have become icons of industrial and community heritage with lasting negative effects on river and stream ecosystems.

The Hopewell Mills dam was removed in 2012 to restore the Mill River in Taunton, Massachusetts. Three dams on this river are being removed.

Efforts to restore migrating fish populations with fish ladders have allowed us to leave the dams and preserve their legacy while trying to accommodate some lost river function. But these aging structures are becoming a hazard for our communities as they reach the end of their functional lives, threatening either to release years of sediment that has accumulated behind them or flooding downstream towns and structures when they fail.

Climate change is adding to the challenge of managing undersized and outdated dams. Unpredictability in our weather and increasing severity of both droughts and floods will require our ecosystems to be more resilient and our wildlife to be more adaptive. This means allowing for more migration, more chances to find refuge, and more diversity in habitat. Mammals and birds can migrate across the landscape and can move in response to shifts in temperature. Fish can migrate only as far as they can swim, and for many, that means as far as the next dam upstream. We are seeing major shifts in ocean fish related to changing ocean temperatures, so we expect populations of freshwater fish to change as well.

The Hopewell Mills dam was removed in 2012 to restore the Mill River in Taunton, Massachusetts. Three dams on this river are being removed.

Thanks to the Industrial Revolution, New England has a larger density of small dams than any other place in the country. More than 600 dams still stand in Rhode Island, more than 3,000 in Massachusetts, and more than 6,000 in Connecticut. Many of these dams are over 200 years old. Working with various local partners, as well as partners in state and federal government, Save The Bay supports dam removal projects that aim to create resilient streams with diverse habitats.

Dam removal has really gathered steam in Massachusetts, where more than 50 dams have been removed in the last 15 years. The Commonwealth has an entire Division of Ecological Restoration that works not only on dams, but on culverts, stream flow and wetland restoration. The state has made a concerted effort to support these projects through capitol authorizations and grant programs.

Rhode Island also has a small habitat restoration fund and supports river restoration projects through state bond referenda, but no dedicated program for riverine habitat restoration exists in state government. Here, local watershed councils and others must initiate fundraising and manage projects. Save The Bay has assisted on several dam removal projects in both Rhode Island and Massachusetts, providing technical, fundraising and outreach support. These projects require multiple partners, from the federal government to local volunteers, and take many years to complete.

Of the 496 animal species federally listed as threatened or endangered, nearly half are freshwater species that have found themselves living in small habitat “islands” due to the cumulative effects of dams, roads and development. This makes them extremely vulnerable to one-time events such as last year’s drought, which dried up small streams in the Taunton watershed and killed many localized populations of rare freshwater mussels.

Diadromous fish—those that migrate between fresh and salt water, like herring, shad, sturgeon, smelt and eels—have all suffered population declines to less than five percent of historic levels, and many rivers lost these species completely. In addition, only about five percent of historic brook trout populations remain and are extremely vulnerable to temperature stress. We have seen many gains in water quality in the last few decades, but we still must remain vigilant in the protection of our most vulnerable freshwater species. The Narragansett Bay watershed depends on us.